We propose to study the basic mechanisms of ion permeation across cell membranes of several types, with particular reference to voltage dependent ionic channels in excitable membranes. (i) Experiments on squid giant axons and isolated neurons from the giant fiber lobe of the squid will use the techniques of voltage and patch-clamping, to investigate the gating mechanism of voltage dependent sodium and potassium channels, two of the basic building blocks of membrane excitability and action potential conduction. Ionic current, gating current, and single channel currents will be measured. The major hypothesis to be tested holds that calcium ion is directly involved in the gating of these channels, and is essential for the maintenance of channel selectivity and integrity. The interaction of calcium ion, the channel gating machinery, and local anesthetic derivatives will be examined, with the dual aim of understanding the mechanism of action of these agents and using them as probes of the structure of the channel gates. (ii) The ionic channels of endocrine cells will be studied, with emphasis on the properties and functional role of two types of calcium channels that coexist in the membranes of pituitary cells. These channels are thought to be intimately involved in the physiological control of secretion by endocrine cells. It is hypothesized that one of these channel types is involved in pacemaking, and the other serves to inject calcium into the cells and thus to promote secretion of hormone. Gating and permeability properties of the channels will be studied in detail. Modulators of channel activity will be sought, and the mechanism of action of the modulators will be determined, with attention to the involvement of intracellular second messengers in modulation. A complete description of the pacemaking machinery and its modulation by physiological transmitters will be attempted. (iii) Ionic channels will be investigated in neurons isolated from the central nervous system of rats. Emphasis will be given to measuring the properties of dendrites. The types and distribution of channels on cell and processes will be determined, using a patch clamp to examine the permeabilities of patches of membrane excised from various regions of the soma and dendrites. (iv) The properties of acetylcholine activated anion channels will be studied in neurons from the giant fiber lobe in squid. The investigations will help in the understanding of a basic physiological component, the ion channel, that plays a role in everything from sensation, to the timing of the heartbeat, to the control of endocrine secretion.